1. Technical Field
The present invention relates to a liquid ejecting head and a liquid ejecting apparatus including the liquid ejecting head, more particularly, relates to a liquid ejecting head and a liquid ejecting apparatus that are usefully applied to a case in which liquid having high viscosity is used.
2. Related Art
As a liquid ejecting apparatus, there is an ink jet recording apparatus including an ink jet recording head. The ink jet recording head includes a plurality of pressure generation chambers, ink supply paths, and nozzle openings. The pressure generation chambers generate pressure for discharging ink droplets by pressure generation units formed by piezoelectric elements, for example. The ink supply paths supply ink individually to each of the pressure generation chambers from a common manifold. The nozzle openings are formed on each of the pressure generation chambers and ink droplets are discharged through the nozzle openings. In the ink jet recording apparatus, discharge energy is applied to ink in the pressure generation chambers communicating with nozzles in response to a print signal so as to cause ink droplets to be discharged through the nozzle openings.
A print target onto which a predetermined text, drawing, or the like is printed by the ink jet recording apparatus of this type includes not only existing paper but also various types of print targets such as plastic and glass and so on. However, existing ink for paper and the like cannot be used sufficiently on a print target having low ink absorbability, such as plastic. That is to say, for example, when printing is performed on plastic with ink which has been used for paper, viscosity (for example, approximately 3.5 (mPa·s) at a normal temperature) of the ink for the paper is too low as ink to be printed on the plastic and there arises a problem in that ink droplets will flow after having landed on the print target depending on cases.
In order to prevent the problem from arising, when printing is performed on a print target having low absorbability, such as plastic, ink having high viscosity (for example, approximately 10.0 (mPa·s) at a normal temperature) has been used.
On the other hand, in particular, in an ink jet recording head in which nozzle portions including nozzle openings are formed on a nozzle plate formed by a silicon single crystal plate among ink jet recording heads, the nozzle portions are formed at two stages in order to lower flow path resistances thereof. That is to say, each nozzle portion in this case has a first nozzle portion and a second nozzle portion. The first nozzle portion is formed at the side of the pressure generation chamber and a cross-sectional area thereof is a first area. The cross-sectional area of the second nozzle portion is a second area which is smaller than the first area. The second nozzle portion is formed to be continuous to the first nozzle portion via a step portion and a front end portion of the second nozzle portion corresponds to a nozzle opening. In the case of the two-stage nozzles, in order to prevent air bubbles from being involved in the nozzle portions during an ink discharge operation, and perform printing with high quality while ensuring discharge stability of ink droplets, the following configuration needs to be employed. That is, a configuration in which vibrating meniscuses are made to be retained on the second nozzle portions so as not to reach the first nozzle portions needs to be employed. Then, the two-stage nozzles of this type are configured such that lengths relating to an ink discharge direction are long at some degree. The flow path resistances of the nozzles which are formed in the silicon single crystal plate in order to make the lengths longer at some degree tend to become large.
When ink having high viscosity is discharged by the ink jet recording head in which the nozzle portions have the two-stage nozzle configurations as described above, discharge performance is inhibited in some cases. This is because the above-described second nozzle portions have not only large inertances but also large flow path resistances.
That is to say, when printing is performed by using ink having high viscosity by the ink jet recording head of the two-stage nozzle system according to an existing technique, there arises the following problems. That is, in such a case, not only an amount of ink droplets to be discharged through nozzle openings becomes small and print quality is adversely affected but also meniscus behavior after discharging is not recovered fast, resulting in an ink discharging cycle being longer, thereby an inhibiting factor for high-speed printing being generated.
The above-described problems are present in not only an ink jet recording head which discharges ink but also a liquid ejecting head which ejects liquid other than ink. In particular, in a liquid head to be used in an industrial application other than printing, there are many opportunities that liquid having high viscosity is ejected and the above-described problems are revealed significantly.
JP-A-2006-290000 (FIG. 1, [0022] to [0027]) is an example of related art.